The present invention relates to a magnetic recording medium and a method for manufacturing the same.
As a high-density recording medium, a metal thin film type magnetic recording tape which does not contain a binder has recently been receiving a lot of attention. Various methods exist for manufacturing metal thin film type magnetic recording tape, including the vacuum deposition method, the sputtering method, the ion-plating method and so on. A magnetic recording tape manufactured by growing crystals of a magnetic metal by one of such methods has a high residual magnetic flux density and little tendency toward self-demagnetization. In a magnetic recording tape manufactured by one of these methods, the thickness of the magnetic layer can be made extremely small as compared with a conventional magnetic recording tape of the coating type which is manufactured by coating magnetic particles mixed with a binder on a base film. For this reason, with the methods mentioned above, a magnetic recording tape is obtained which is capable of a long recording time and suitable for high-density recording (the thinner the magnetic recording layer, the better the high frequency response during recording and playback).
Despite the advantages as described above, the magnetic recording tape obtained by forming a ferromagnetic metal thin film by vacuum deposition or sputtering is subject to a drawback which is not encountered in the coating type magnetic recording tape. More specifically, the metal thin film type magnetic recording tape has a significantly greater stiffness. A metal thin film type magnetic recording tape of substantially the same output as a coating type magnetic recording tape has a very small thickness but has a stiffness almost twice as much as that of the latter. In other words, the metal thin film type magnetic recording tape is too stiff and lacks flexibility. For this reason, good head touch is hard to obtain and tape travel is unstable with the metal thin film type magnetic recording tape.
A prior art technique has been proposed in Japanese Patent Disclosure No. 53-73,109 to solve this problem. According to this prior art technique, a nonmagnetic metal having a low Young's modulus is mixed in the ferromagnetic metal film. This prior art technique attempts to reduce the stiffness of the magnetic recording tape by adopting a composite magnetic film. With this prior art technique, it is indeed possible to manufacture a metal thin film type magnetic recording tape which has relatively little stiffness. However, this technique is also subject to some drawbacks. Since the composite magnetic film is formed by the two-component deposition method, it is difficult to form a magnetic film of uniform composition. In addition to this, the low stiffness intended by the applicant of the present application cannot be achieved by simply mixing a metal having a low Young's modulus in the ferromagnetic metal film.
The metal thin film type magnetic recording tape is also subject to the following problems. When the magnetic metal recrystallizes on the base film, internal stress is generated and the film curls. Furthermore, the surface of the thin magnetic layer formed by the vacuum deposition method or the like is indented when it is observed microscopically. Curling of the film adversely affects the head touch or stable tape travel, and the indented surface of the tape increases the level fluctuations in high frequency range.
Another prior art technique is proposed in Japanese Patent Disclosure No. 54-155,012 which may look similar to the present invention. According to this prior art technique, a high polymer thin film is formed on a base film. After calendering, a magnetic film is formed on the high polymer thin film. This method attempts to improve the mechanical strength of the overall film while maintaining good adhesion of the magnetic film. However, this technique does not deal with the technical subject matter of the present invention. The present invention totally differs from this prior art technique in the manufacturing steps after the formation of said high polymer thin film.